Flow control valve capable of adjusting fluid flow characteristics in accordance with a position of a valve element in a bore

ABSTRACT

A flow control valve has body ( 20 ) containing a “bucket” shaped valve element ( 1 ) that moves in a bore ( 2 ). The valve element ( 1 ) has a discharge orifice ( 8 ) through which a needle valve ( 9 ) projects. Movement of the valve element ( 1 ) within the bore ( 2 ) adjusts the annular clearance between the orifice ( 8 ) and the needle ( 9 ) thereby varying the pressure drop across the valve element ( 1 ) and the rate of the main flow through the valve. The inlet ( 4   a ) to the body ( 20 ) is located upstream of the valve element. With this arrangement, the spill flow rate is adjusted by movement of the valve element ( 1 ) within the bore ( 2 ). However, in all cases the main flow of fluid passes through the orifice ( 8 ) of the valve element ( 1 ) through the bore ( 2 ) to the outlet ( 10 ), thereby avoiding the formation of stagnant “pools” of fluid within the bore ( 2 ) of the flow control valve.

BACKGROUND OF THE INVENTION

The present invention relates to a flow control valve, and in particularto a flow control valve having improved flow control characteristicsresulting in improved output flow rates and pressures. The valve isparticularly suited to pumps which pump fluids, predominantly containingliquids.

In a known pump assembly, the discharge from the pumping element flowsto a valve arrangement having a valve element nominally floating in abore. The valve arrangement includes a cavity into which the dischargefrom the pumping element flows. The cavity includes a discharge orificethrough which fluid flows from the cavity with a pressure drop beingestablished across the discharge orifice. The cavity has a furtherseparate opening into the bore in which the valve element is “floating”.On the downstream side of the discharge orifice, a passage runs to theside of the bore, distant from the cavity, relative to the valveelement. Thus, the valve element is balanced with two pressures, thepumping pressure (of the fluid in the cavity) acting on one end and thedischarge pressure (determined by the discharge orifice) applied to theother end. A biasing member in the form of a spring is also provided tobias the valve element towards the cavity, whilst the pressuredifference across the valve element acts to bias the valve element awayfrom the cavity. In this way the valve arrangement is located in a borewhich communicates across the discharge orifice of the cavity which inturn means that the valve element is separate from the dischargeorifice.

In this arrangement, if the pumping pressure exceeds the dischargepressure by more than a predetermined amount, the valve element becomessufficiently displaced from its position of zero displacement (i.e. itsposition when there is no pressure difference across the valve element)to open a channel to a spill port which directs fluid from the cavityback to the inlet of the pump. The difficulty with this arrangement isthat there is insufficient control of the discharge flow rate, from thedischarge orifice, with respect to pump speed and pressure. In fact,with such an arrangement, the discharge flow rate tends to increase withboth pump speed and pressure.

The disadvantage described above with the conventional valve arrangementcan be mitigated to an extent by forming a small recess in the front ofthe valve element and by suitable shaping of the spill port.Additionally, the valve arrangement may be improved by providing a“needle” (a rod having a profiled shape) on the end of the valve elementwhich moves in the discharge orifice formed in a discharge plug alignedwith the valve element, such that the annular area between the needleand the circumference of the discharge orifice varies with the movementof the valve element in the bore. The problems with this arrangement arethat the needle position is fixed relative to the position of the valveelement, the needle is expensive to manufacture and the region withinthe bore where the discharge pressure acts has an almost stagnant poolof fluid, where problems of contamination can develop. The valve elementmust also be further increased in complexity because of the need toincorporate within it a pressure relief valve, which opens at a highpressure setting (e.g. approximately 50-70 bars) to relieve pressureback to the pump inlet in the event of overloading the output.

SUMMARY OF THE INVENTION

The present invention seeks to provide a flow control valve whichaddresses the above identified disadvantages and provides an improvementover the prior art referred to.

According to the present invention there is provided a flow controlvalve comprising a body, a bore having first and second axial ends, thebore being formed within the body of the valve; a valve element movablylocated within the bore; an inlet in communication with the first axialend of the bore; an outlet in communication with the second axial end ofthe bore; adjustment means for adjusting at least one characteristic ofthe flow of fluid through the flow control valve in accordance with theposition of the valve element within the bore; and a discharge orificeformed in the valve element for establishing a pressure differentialacross the valve element between the first and second axial ends of thebore.

With the present invention, therefore, the valve element, in combinationwith the discharge orifice in the valve element, provides the primaryroute through the valve to the outlet for discharging fluid, i.e. themain flow of fluid through the valve passes from the inlet into thevalve element via the discharge orifice and out of the valve element viaits open end to the outlet. This avoids the formation of stagnant“pools” of fluid either upstream or downstream of the valve element, asthe majority of the fluid generally flows along the main axis of theflow control valve and is not diverted into a side channel.

The adjustment means preferably includes a spill port having an openinginto the first axial end of the bore, the valve element being slidableaxially within the bore between a first position, in which the openingof the spill port is blocked by the valve element, and a second positionin which the opening to the spill port from the first axial end of thebore is not blocked by the valve element. In this way, a substantiallyconstant pressure drop across the discharge orifice may be maintained.

Alternatively, or additionally, the adjustment means may include aneedle which is positioned so as to project through the dischargeorifice such that movement of the valve element within the bore causesrelative movement between the discharge orifice and the needle whichrelative movement alters the clearance between the needle and dischargeorifice. In this context, the needle functions as a variable closuremember in relation to which the valve element and hence the dischargeorifice move such that the relative movement between the valve elementand the variable closure member alters the volume of fluid which flowsper second through the discharge orifice. It is generally envisaged thatthe variable closure member will take the form of a shaped rod theexternal cross-sectional area of which varies along its length and whichis mounted so that the free end of the rod projects through thedischarge orifice such that relative axial movement between the valveelement and the rod will cause the annular clearance between the rod andthe discharge orifice to vary in size thus varying the volume of fluidwhich can flow through the clearance per second.

By mounting the needle so that the valve element (and thus, in thepresent invention, the discharge orifice) moves relative to it, there ismuch greater flexibility in the scope for design variations of theneedle as it need not be attached to the valve element. For example, theneedle may be rigidly fitted concentric or eccentric with the dischargeorifice, it may be permitted to fall to one side of the dischargeorifice to improve the consistency of flow restriction, or it may bemounted with flexibility axially and/or radially (with a device such asa spring, a pad or another valve) to increase the variables availablefor control of the rate of flow of fluid through the discharge orifice.There are also other advantages to the arrangement of the presentinvention such as the avoidance of the near stagnant area of fluid atthe second axial end of the bore, and also, the needle is much cheaperand easier to manufacture. As the output or discharge of the flowcontrol valve is straight through the discharge orifice in the valveelement, no communication channel needs to be made to the second axialend of the bore from the downstream side of the discharge orifice, as isthe case in the prior art, and so fluid and consequent pressure loss maybe reduced.

By providing a small hole bored through the needle a safety pressurerelief valve may be positioned in the closing plug or at any convenientlocation remote from the bore which senses the fluid pressure in thesecond axial end of the bore or, in other words, the discharge or outputpressure of the flow control valve. Operation of this safety reliefvalve both increases the flow of fluid through the discharge orifice andcauses the valve element to move towards its second position thusopening the spill port and generally preventing any excess pressurebuild-up without the requirement of a complicated and expensive pressurerelease valve in the valve element itself. The dimensions of the holebored through the needle can be selected to provide a pressure drop fromone end of the hole to the other which may be useful for shaping thecontrol characteristics of the safety pressure relief valve duringspilling of fluid from the first axial end of the bore into the spillport. The safety pressure relief valve may be fitted anywhere in thevalve body provided it is in communication with the downstream side ofthe discharge orifice. Preferably the safety pressure relief valve isarranged to spill fluid through the safety pressure relief valvedirectly into the inlet of the pump from the pump discharge of whichfluid to the inlet of the flow control valve is driven. Thus, the safetypressure relief valve may be fitted in the valve bore to communicatedirectly with the second axial end of the bore (the needle hole is thennot required), or somewhere else along the output of the flow controlvalve without there being a significant pressure drop from the outputflow to the safety pressure relief valve. However, with such anarrangement the additional control option provided by the pressure dropis lost.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be better understood anembodiment thereof will now be described by way of example only withreference to the accompanying drawings, in which FIG. 1, is across-sectional view through a flow control valve in accordance with thepresent invention. FIG. 2 shows the valve as is suited for use as a flowcontrol valve on the outlet of a fluid pump. In particular, the valvemay be used with the type of pump having a carrier mounted on a shaftfor rotation therewith, a plurality of pumping elements mounted radiallyextendibly within or on the carrier, a cam ring whose internal surfaceis followed by the pumping elements as the shaft, carrier and pumpingelements rotate with respect to the cam ring, and which is not co-axialwith the carrier, a pump inlet and a pump outlet, and wherein the flowcontrol valve is connected to the pump outlet. FIG. 3 illustrates avalve similar to FIG. 1 but showing a needle mounted on a flexibleplatform.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A valve body 20 contains a “bucket” shaped valve element 1 which movesin a close fitting bore 2. Fluid is pumped into a radial passage 25 andinto a cavity 3 in a first axial end of the bore 2, through holes 4 a ina spacer 4, which holes 4 a thus form an inlet to the cavity 3 of theflow control valve. The pumped, pressurized fluid may move the valveelement 1 against the force of a precompressed spring 5 until the fluidin the cavity 3 starts to spill through entrance 6 into a return orspill port 7. A fixed needle 9 is mounted in the body 20 of the valveand projects through a cavity discharge orifice 8 formed within thevalve element 1. Movement of the valve element 1 in the bore 2 causesthe annular clearance between the cavity discharge orifice 8 and thefixed needle 9, which has a tapered profile, to change incross-sectional area, such that the pressure drop across the valveelement 1 from a first axial end 21 of the bore 2 to a second axial end22 of the bore 2 varies. The movement of the valve element 1 alsomodifies the spill flow rate through entrance 6 into return port 7. Bysuitably selecting the profile of the needle 9 and the shape of theentrance 6 to the return port 7 the desired output flow rate via cavity10, which thus forms an outlet of the valve, may be achieved.

Also shown in FIG. 1 is a capillary hole 11 bored through the needle 9which feeds pressure to a cavity 12 by way of a safety pressure reliefvalve 23 mounted in a plug 13, such that relief flow through thecapillary hole 11 causes the flow rate through the discharge valve 8 toincrease. At the same time, the reduction in pressure in the secondaxial end 22 of the bore 2 increases the pressure drop between the firstaxial end 21 of the bore 2 and the second axial end 22 of the bore 2which in turn causes the valve element 1 to move away from the cavity 3thus opening the valve edge of the entrance 6 to the return port 7 to alarger extent, which in turn allows the bulk of the excess fluid fromthe cavity 3 to flow out of the flow control valve and, via a suitablepassage (not shown), to the pump return.

The plug 13 secures the flow control valve assembly and spring 5 withinthe bore 2. The most important elements of the flow control valve whosedimensions may be altered in order to control the flow characteristicsof the valve are the relative sizes of the discharge orifice 8, thecapillary hole 11, the opening 6 to the return port 7 and the profile ofthe needle 9; the viscosity of the fluid being pumped through the valvewill also affect the flow characteristics of the valve.

As shown in FIG. 3, the needle 9 may be mounted on a flexible platform26 which is attached to the body of the valve. The flexible platform canbe used to move the needle axially, radially or both against theresistance of spring 28 by the pressure difference between the cavity 3and cavity 27, so that the valve element and needle 9 may be caused tomove simultaneously or independently, depending on the springcharacteristics. This acts as a further control of the fluid ratethrough the valve. Also, the needle need not be concentric with eitherthe bore or the discharge orifice. An eccentric position may affordimproved consistency of flow restriction.

It will be apparent to a person skilled in the art that alternativearrangements of the valve concept may be employed without departing fromthe scope of the present invention as set out in the claims. Inparticular, the shape of the needle may be adjusted as required. Thevalve element 1 needs only to “seal” (reduce leakage to acceptablevalues compared with that flowing through the annular clearance betweenthe discharge orifice 8 and the needle 9) so it may take any shapecompatible with the bore shape provided it is free to move axially. Theoutput cavity 10 may be connected to an outlet fitting which mayincorporate a second cap to facilitate boring and spring mounting. Thechoice of materials used essentially depends on the strength, machiningcost and fluid compatibility of the various elements of the flow controlvalve, but irons, steels or aluminium alloys are preferred. Mechanicalforce devices are most conveniently fitted as coil springs, but are notexclusively so. The valve discharge orifice shape is normally a constantdiameter bore, but could be some other variable shape. The valve elementmay be moved with electrical or mechanical devices controlled by thepressures in addition to or instead of using a mechanical force devicesuch as a spring. Finally, the term “fluid” is used in a generic senseto include any liquid, possibly containing free gas, but in practice alubricating fluid, for low friction wear, will be preferred. Details ofthe safety pressure relief valve and its location are immaterial exceptas how they require features in the flow control valve to operate.

What is claimed is:
 1. A flow control valve comprising a body; a borehaving first and second axial ends, the bore being formed within thebody of the valve; a valve element movably located within the bore; aninlet in communication with the first axial end of the bore; an outletin communication with the second axial end of the bore; adjustment meansfor adjusting at least one characteristic of the flow of fluid throughthe flow control valve in accordance with the position of the valveelement within the bore; and a discharge orifice formed in the valveelement for establishing a pressure differential across the valveelement between the first and second axial ends of the bore; wherein theadjustment means includes a spill port having an opening into the firstaxial end of the bore and wherein the valve element is slidable axiallywithin the bore, between the inlet and the outlet, between a firstposition, in which the opening of the spill port is blocked by the valveelement, and a second position in which the opening to the spill portfrom the first axial end of the bore is not blocked by the valveelement, the valve further comprising biasing means for biasing thevalve element towards said first position, said biasing means beingdisposed in the fluid flow path between the discharge orifice and theoutlet so as to reduce stagnant regions in the valve.
 2. A flow controlvalve as claimed in claim 1, wherein the adjustment means furtherincludes a variable closure member, the valve element being arranged tomove relative to the variable closure member whereby the open area ofthe discharge orifice is altered.
 3. A flow control valve as claimed inclaim 2, wherein the variable closure member is in the form of a needlewhich is positioned so as to project through the discharge orifice, thearrangement of the needle with respect to the discharge orifice beingsuch that movement of the valve element in the bore causes relativemovement between the discharge orifice and the needle so as to alter theclearance between the needle and the discharge orifice.
 4. A flowcontrol valve as claimed in claim 3, wherein said needle has a holebored therethrough whereby the pressure within the second axial end ofthe bore is communicated to a safety pressure relief valve forpreventing dangerously high pressures from developing in the valve.
 5. Aflow control valve as claimed in claim 3, wherein the externalcross-sectional area of the needle varies along its length.
 6. A flowcontrol valve as claimed in claim 3, wherein the needle is mounted on aflexible platform which is attached to the body of the valve.
 7. A flowcontrol valve as claimed in claim 6, wherein the flexible platformcomprises a spring, a soft pad, a pressure controlled device or asimilar device which permits the needle to move axially, radially orboth as required to control the rate of flow of fluid through thedischarge orifice.
 8. A flow control valve as claimed in claim 1 furthercomprising a safety pressure relief valve communicating with the secondaxial end of the bore whereby, when the safety pressure relief valve isopened, the flow of fluid through the discharge orifice is increasedcausing the flow control valve to open further and act a s a secondaryrelief valve by increasing communication between the inlet and the spillport.
 9. A pump assembly including a flow control valve as claimed inany one of the preceding claims, said pump assembly comprising a carriermounted on a shaft for rotation therewith, a plurality of pumpingelements mounted radially extendibly within or on the carrier, a camring which internal surface is followed by the pumping elements as theshaft, carrier and pumping elements rotate with respect to the cam ring,and which is eccentric with regard to the axis of the carrier, a pumpinlet and a pump outlet, and wherein the flow control valve is connectedto the pump outlet.
 10. A flow control valve as claimed in claim 2,further comprising a safety pressure relief valve communicating with thesecond axial end of the bore whereby, when the safety pressure reliefvalve is opened, the flow of fluid through the discharge orifice isincreased causing the flow control valve to open further and act as asecondary relief valve by increasing communication between the inlet andthe spill port.
 11. A flow control valve as claimed in claim 3, furthercomprising a safety pressure relief valve communicating with the secondaxial end of the bore whereby, when the safety pressure relief valve isopened, the flow of fluid through the discharge orifice is increasedcausing the flow control valve to open further and act as a secondaryrelief valve by increasing communication between the inlet and the spillport.
 12. A flow control valve as claimed in claim 5, wherein the needleis mounted on a flexible platform which is attached to the body of thevalve.
 13. A flow control valve as claimed in claim 5, wherein saidneedle has a hole bored therethrough whereby the pressure within thesecond axial end of the bore is communicated to a safety pressure reliefvalve for preventing dangerously high pressures from developing in thevalve.
 14. A flow control valve as claimed in claim 5, furthercomprising a safety pressure relief valve communicating with the secondaxial end of the bore whereby, when the safety pressure relief valve isopened, the flow of fluid through the discharge orifice is increasedcausing the flow control valve to open further and act as a secondaryrelief valve by increasing communication between the inlet and the spillport.
 15. A flow control valve as claimed in claim 6, wherein saidneedle has a hole bored therethrough whereby the pressure within thesecond axial end of the bore is communicated to a safety pressure reliefvalve for preventing dangerously high pressures from developing in thevalve.
 16. A flow control valve as claimed in claim 6, furthercomprising a safety pressure relief valve communicating with the secondaxial and of the bore whereby, when the safety pressure relief valve isopened, the flow of fluid through the discharge orifice is increasedcausing the flow control valve to open further and act as a secondaryrelief valve by increasing communication between the inlet and the spillport.
 17. A flow control valve as claimed in claim 7, wherein saidneedle has a hole bored therethrough whereby the pressure within thesecond axial end of the bore is communicated to a safety pressure reliefvalve for preventing dangerously high pressures from developing in thevalve.
 18. A flow control valve as claimed in claim 7, furthercomprising a safety pressure relief valve communicating with the secondaxial end of the bore whereby, when the safety pressure relief valve isopened, the flow of fluid through the discharge orifice is increasedcausing the flow control valve to open further and act as a secondaryrelief valve by increasing communication between the inlet and the spillport.
 19. A flow control valve comprising a body; a bore having firstand second axial ends, the bore being formed within the body of thevalve; a valve element movably located within the bore; an inlet incommunication with the first axial end of the bore; an outlet incommunication with the second axial end of the bore; adjustment meansfor adjusting at least one characteristic of the flow of fluid throughthe flow control valve in accordance with the position of the valveelement within the bore; and a discharge orifice formed in the valveelement for establishing a pressure differential across the valveelement between the first and second axial ends of the bore; wherein themajority of the fluid flows through the discharge orifice to the outletsubstantially along the primary axis of the bore; the valve furthercomprising biasing means for biasing the valve element, said biasingmeans being disposed between the discharge orifice and the outlet in thefluid flow path so as to reduce stagnant regions in the valve.